1. Field of the Invention
The present invention relates to a motor drive, and more specifically relates to a motor drive having a function for preventing damage from spreading, even if power is supplied again to the motor drive that has been damaged by an abnormality.
2. Description of Related Art
As a conventional art, there are known motor drives that, in the event of an overcurrent condition of a power element inside the motor drives, store the presence or absence of an alarm and disable the next and later power-on to avoid secondary damage to the motor drives.
For example, there are known motor drives having a secondary damage prevention circuit for a main circuit of the motor drive. The secondary damage prevention circuit is provided with a means for detecting an overcurrent through the main circuit of the motor drive. Upon detecting the overcurrent flowing through the main circuit, the secondary damage prevention circuit issues an overcurrent alarm, as well as storing the issue of the alarm, and disables the next and later power-on (for example, Japanese Patent Application Laid-Open No. 9-46891).
FIG. 1 is a block diagram of a conventional motor drive. In the conventional motor drive shown in FIG. 1, an overcurrent protection circuit for a converter main circuit 1002 includes an overcurrent detection circuit 1004, an alarm latch circuit 1005, an alarm reset circuit 1006, an alarm evaluation circuit 1007, an MCC drive circuit 1008, an MCC drive coil 1009, and a fuse blowout circuit 1010.
A control circuit (main circuit MCC) 1001 controls an alternating current power supply from a power source 1020 to the converter main circuit 1002. The alternating current power supplied to the converter main circuit 1002 is converted into direct current power, smoothed by a DC link capacitor 1012, and then inputted to an inverter main circuit 1003 for driving a motor (not shown). The overcurrent detection circuit 1004 has a first detection level to detect an overcurrent passing through the control circuit 1001 and a second detection level below the first detection level. The first memory means (fuse blowout circuit) 1010 stores a detection value using the first detection level. The second memory means (alarm latch circuit) 1005 stores a detection value using the second detection level in a resettable manner. The secondary damage prevention circuit for the converter main circuit 1002 controls the control circuit 1001 based on the memory contents of the first memory means 1010 and second memory means 1005, so as to prevent the reclosing of the control circuit 1001 using alarm reset.
This conventional motor drive aims only at protecting the converter main circuit 1002 provided in the secondary damage prevention circuit, and does not protect component parts provided outside the secondary damage prevention circuit such as the main circuit MCC 1001. Also, in the conventional motor drive, an alarm is issued by focusing only on the overcurrent, as a factor for the secondary damage to the motor drive. Thus, there is a problem that the conventional motor drive does not provide protection against other types of abnormalities.
Furthermore, this conventional motor drive is too sensitive to the occurrence of abnormalities, because, as shown in FIG. 2, once the overcurrent detection circuit 1004 detects an abnormality, a fuse 1011 melts in the fuse blowout circuit 1010 to disable the next or later power-on of the power source 1020.